IBX- Mass Transfer 10-12 Flashcards
Steam distillation is used for separation of high boiling
substances from non-volatile impurities.
volatile impurity from still higher boiling substances.
both (a) and (b).
neither (a) nor (b).
both (a) and (b).
The feed to fractionating column is changed from saturated vapour to saturated liquid. If the separation and reflux ratio remains unchanged, the number of ideal stages will
increase
decrease
remains same
depend on saturated boiling point; may increase or decrease
increase
Rose oil is extracted from rose leaves using __________ distillation.
high pressure
low pressure
extractive
steam
steam
Hypersorption refers to a __________ process.
fixed bed absorption
moving bed absorption
fixed bed adsorption
moving bed adsorption
moving bed adsorption
figure
…
Extraction of coffee from its seed is done by
liquid-liquid extraction.
leaching.
extractive distillation.
steam distillation.
leaching.
In azeotropic mixture, the equilibrium vapour composition is
more than liquid composition.
less than liquid composition.
same as liquid composition.
independent of pressure.
same as liquid composition.
With lapse of time, the overhead composition of light component in case of batch distillation with constant reflux
increases
decreases
remains same
may increase or decrease ; depends on system.
decreases
Lewis number, which is important in problems involving simultaneous heat and mass transfer, is the ratio of
mass diffusivity to momentum diffusivity.
thermal diffusivity to mass diffusivity.
momentum diffusivity to thermal diffusivity.
none of these.
thermal diffusivity to mass diffusivity.
According to the film theory of mass transfer, the mass transfer co-efficient is proportional to (where, D = molecular diffusivity)
D
D^2
D^0.5
1/D
D
Dry bulb temperature of the gas is __________ the wet bulb temperature.
less than
more than
equal to
none of these
more than
Decoction refers to the use of solvent
at ambient temperature
at its boiling point
in its vapor form
none of these
at its boiling point
Flash distillation is suitable for separating the constituents of a binary system, which
form minimum boiling azeotrope.
have very wide boiling points.
have very close boiling points.
form constant boiling azeotrope.
have very wide boiling points.
The ratio of Murphree plate efficiency to point efficiency is 1 in a __________ flow model.
plug
perfectly mixed
both (a) & (b)
neither (a) nor (b)
perfectly mixed
The rough value of diffusion co-efficient of water vapor into air at 25°C may be about __________ cm2/sec.
0.25
2.5
1.25
0.0025
0.25
Flooding in a column results due to
high pressure drop
low pressure drop
low velocity of the liquid
high temperature
high pressure drop
Which of the following gas-liquid contacting devices incurs the least pressure drop for a particular duty ?
Grid tray tower
Perforated tray tower
Wetted wall tower
Bubble cap tower
Wetted wall tower
A liquid mixture contains 30% o-xylene, 60% p-xylene and 10%. m-xylene (all percentages in w/w). Which of the following statements would be true in respect of this mixture?
The mixture exhibits an azeotrope at 101.3 kPa.
The composition of the mixture, in percent by volume is: o-xylene 30, p-xylene 60. and m-xylene 10.
The composition of the mixture in mole percent is: o-xylene 30, p-xylene 60 and m-xyoene 10.
The mixture contain optical isomers.
The mixture exhibits an azeotrope at 101.3 kPa.
Unsaturated air (with dry bulb temperature and dew point being 35°C and 18°C respectively) is passed through a water spray chamber maintained at 15°C. The air will be cooled
and humidified.
and dehumidified with increase in wet bulb temperature.
at the same relative humidity.
and dehumidified with decrease in wet bulb temperature.
and dehumidified with decrease in wet bulb temperature.
The process employing desorption of the absorbed solute by a solvent is called
elution
osmosis
reverse osmosis
sublimation
elution
If the overall efficiency and Murphree plate efficiency are equal, then both the equilibrium and operating lines are
straight
parallel
both (a) & (b)
neither (a) nor (b)
both (a) & (b)
Which of the following operations does not involve leaching ?
Dissolving gold from ores.
Dissolving pharmaceutical products from bark or roots.
Dissolving sugar from the cells of the beet.
Removing nicotine from its water solution by kerosene.
Removing nicotine from its water solution by kerosene.
The recovery of pencillin from the acidified fermentation broth is done by
distillation
evaporation
absorption
liquid extraction
liquid extraction
Unit operation involved in the prilling of urea is
evaporation
drying
crystallisation
both (b) and (c)
both (b) and (c)
Molecular seives are porous
alumina.
silica.
synthetic zeolites crystals/metal alumino-silicates.
none of these.
synthetic zeolites crystals/metal alumino-silicates.
Calcium ammonium nitrate (a fertiliser) is dried in a __________ dryer.
rotary
vacuum
tunnel
tray
rotary
A binary mixture of benzene and cyclohexane is separated by
flash vaporisation
extractive distillation
solvent extraction
ordinary distillation
extractive distillation
Component A is diffusing in a medium B. The flux NA relative to a stationary point is equal to the flux due to molecular difusion, if
mass transfer is accompanied by reaction.
diffusion of A is in stagnant medium B.
molecular mean free path is high.
there is equimolar counter diffusion.
There is equimolar counter diffusion.
Cox chart is useful in the design of
distillation column
evaporator
dryer
crystalliser
distillation column
Dew point of an air-water vapor mixture
decreases with decrease in pressure.
at constant humidity & total pressure is fixed.
corresponding to any point on the humidity chart is obtained by projecting a line through this point parallel to the temperature axis and to the saturation curve.
all ‘a’, ‘b’ & ‘c’.
all ‘a’, ‘b’ & ‘c’.
Can a cooling tower cool water below the wet bulb temperature of inlet air ?
yes
no
yes ; but height of cooling tower will be prohibitively high.
yes ; but the air flow rate should be excessively high.
no
The solvent used in liquid-liquid extraction should have __________ less than one.
selectivity
distribution co-efficient
both (a) and (b)
neither (a) nor (b).
neither (a) nor (b).
The suitable evaporator for concentration of foaming liquids is a __________ evaporator.
long tube
short tube
vacuum
falling film
long tube
The ratio of Murphree plate efficiency to point efficiency is always > 1 in a __________ flow model.
plug
perfectly mixed
both (a) & (b)
neither (a) nor (b)
plug
Tea percolation employs
liquid-liquid extraction
leaching
absorption
none of these
leaching
Which of the following assumes constant molal vaporisation and overflow ?
McCabe-Thiele method
Ponchan-Savarit method
Enthalpy concentration method
Plate absorption column
McCabe-Thiele method
Absorption factor, for a fixed degree of absorption from a fixed amount of gas should be
1
> 1
< 1
≤ 1
> 1
Selectivity of the solvent used in solvent extraction should be
1
> 1
< 1
0
> 1
Pick out the wrong statement pertaining to leaching.
Fine solids can not be leached in a Pachuka tank.
Door classifier can be used for leaching of coarse solids.
Vegetable seeds can be leached in either of Bollman extractor, Rotocel or Kennedy extractor.
Very high temperature is not needed for the leaching of sugar beet.
Fine solids can not be leached in a Pachuka tank.
Wet bulb and dry bulb temperatures becomes identical at __________ percent saturation curve.
100
50
78
none of these
100
NSc/NPr is called the
psychrometric ratio
Lewis number
Sherwood number
Stantan number
Lewis number
McCabe-Thiele method
uses molal units for material and energy balance.
uses weight fractions to express liquid and vapour composition.
can use any type of units.
is more accurate than Ponchan-Savarit method.
uses molal units for material and energy balance.
The film penetration model of mass transfer was enunciated by
Gilliland
Toor and Marchello
Stefan
Fick
Toor and Marchello
The most economical range of absorption factor is
0 to 0.5
0 to 3
1.25 to 2
5 to 15
1.25 to 2
Channelling is most severe
in towers packed with stacked packing.
in towers packed randomly with crushed solids.
in dumped packing of regular units.
at very high liquid flow rate.
in towers packed with stacked packing.
Out of two equilibrium curves, first one lies above the diagonal and the second lies below the diagonal in the x-y plot. It means that separation by distillation is
not possible in the second case unless vacuum is applied.
not possible in the second case unless high pressure is applied.
more readily done in the second case compared to first one.
none of these
more readily done in the second case compared to first one.
‘ADDUCTS’ and ‘CLATHRATES’ are used in case of
extractive distillation.
crystallisation.
absorption.
none of these.
crystallisation.
Separation of the isotopes of helium for scientific investigations is done by
reverse osmosis
thermal diffusion
leaching
solvent extraction
thermal diffusion
In case of __________ distillation, a solvent is added to alter the relative volatility of the mixture to be separated.
molecular
azeotropic
extractive
flash.
extractive
Adsorption is an unit operation which generally involves __________ systems.
liquid-solid
gas-solid
fluid-solid
solid-solid
fluid-solid
In a binary system, separation is very efficient, when the relative volatility is
1
> 1
< 1
0.5
> 1
Fenske-Underwood equation used for calculating the minimum number of theoretical plates in distillation column is valid for
constant molal overflow
total reflux
constant relative volatility
all (a), (b) and (c)
all (a), (b) and (c)
The binary diffusivity in gases does not depend upon the
pressure
temperature
nature of the components
none of these
none of these
Berl saddle made of carbon cannot be used for
alkalis
SO2
H2SO4
oxidising atmosphere
oxidising atmosphere
1 kg of a saturated aqueous solution of a highly soluble component A at 60°C is cooled to 25°C. The solubility limits of A are (0.6 kgA/kg water) at 60°C and (0.2 kgA/kg water) at 25°C. The amount in kg of the crystals formed is
0.4
0.25
0.2
0.175
0.2
During drying of a solid, the critical moisture content increases with
decreased drying rate
increased thickness of the solid
increased drying rate
both (b) and (c).
both (b) and (c).
Priming in a distillation column
results from very low gas velocity.
is desirable from point efficiency consideration.
is characterised by the presence of foam throughout the space between trays.
reduces the overall pressure drop.
is characterised by the presence of foam throughout the space between trays.
The commonly used solvent in supercritical extraction is
methyl ethyl ketone.
water.
carbon tetrachloride.
carbon dioxide.
carbon dioxide.
When the liquid over a plate is of uniform concentration, then
Murphree efficiency > point efficiency.
Murphree efficiency < point efficiency.
Murphree efficiency = point efficiency.
Murphree efficiency ≠ point efficiency.
Murphree efficiency = point efficiency.
In saturated gas, the
vapour is in equilibrium with the liquid at the gas temperature.
vapour is in equilibrium with the liquid at the room temperature.
partial pressure of vapour equals the vapour pressure of the liquid at room temperature.
none of these.
vapour is in equilibrium with the liquid at the gas temperature.
As per Gilliland’s equation, the diffusivity is
directly proportional to ‘T^1.5’.
inversely proportional to ‘P’.
dependent on the molecular volume & molecular weight of components.
all ‘a’, ‘b’ & ‘c’.
all ‘a’, ‘b’ & ‘c’.
Pick out the wrong statement.
When the concentration difference for the mass transfer becomes zero at the bottom of the gas absorption tower, then the upper end of the operating line touches the equilibrium curve.
The average distance between the operating line and equilibrium line is large, when the liquid-gas ratio is also large in case of a counter current gas absorption tower.
The operating line lies above the equilibrium curve in case of a gas desorber.
With decrease in the liquid flow rate for a fixed gas flow rate, the slope of the operating line decreases, in case of gas absorption process.
The operating line lies above the equilibrium curve in case of a gas desorber.
A mixture of 10% C6H6 vapour in air at 25°C and 750 mm Hg has a dew point of 20°C. Its dew point at 30°C and 700 mm Hg will be around __________ °C.
21.7
20
27.3
18.7
18.7
Which of the following is not fixed by the process requirements, in the design of absorbers ?
Flow rate of the entering gas.
Composition of the entering liquid.
Terminal concentrations of gas stream.
None of these.
None of these.
If the amount of the steam used in steam distillation is increased, the temperature of distillation
increases
decreases
remains unchanged
depends on relative volatility
decreases
Moisture in a solid exerting an equilibrium vapour pressure equal to that of the pure liquid at the same temperature is called the __________ moisture.
unbound
critical
free
bound
unbound
Inside the distillation columns, the
highest temperatures is near the feed plate.
driving force for the liquid flow is its weight.
vapors are not always at their dew points.
all (a), (b) and (c)
driving force for the liquid flow is its weight.
When the psychometric ratio is __________ then the adiabatic saturation temperature and wet bulb temperature becomes equal.
1
< 1
> 1
∞
1
Desirable value of absorption factor in an absorber is
1
< 1
> 1
0.5
> 1
Refractory bricks are usually dried in a __________ dryer.
tray
tunnel
conveyor
festoon
tunnel
For __________ drying, the effects of velocity, temperature and humidity of the gas and the thickness of the solid are the same.
unsaturated surface
constant rate
both (a) and (b)
neither (a) nor (b).
both (a) and (b)
What is the degree of freedom of an absorption process in which only one component is transferred between phases ?
3
2
4
1
3
Sticky material can be dried in a __________ dryer.
tray
rotary
fluidised bed
none of these
tray
Langmuir equation is associated with
leaching
adsorption
steam distillation
multicomponent absorption.
adsorption
During the constant rate period of drying of a solid,
increased air humidity decreases the rate of drying.
increasing the air temperature decreases the drying rate.
surface evaporation of unbound moisture occurs.
none of these.
surface evaporation of unbound moisture occurs.
At a fixed total pressure, humidity depends only on the
partial pressure of vapour in the mixture.
heat capacity of the vapour.
density of the vapour.
none of these.
partial pressure of vapour in the mixture.
If moisture content of solid on dry basis is X, then the same on wet basis is
X/X+1
X/X-1
1+X/X
1-X/X
X/X+1
Flash distillation is
same as differential distillation.
used for multicomponent systems like crude refining.
same as simple distillation.
most useful for handling binary systems.
used for multicomponent systems like crude refining.
__________ developed the film theory.
Higbie
Fick
Ergun
Levenspeil
Higbie
For absorbers, high pressure drop results in
increased efficiency.
decreased efficiency.
high operating cost.
better gas liquid contact.
high operating cost.
Which of the following parameters remains almost constant during adiabatic saturation of unsaturated air ?
Dry bulb temperature
Dew point
Wet bulb temperature
None of these parameters
Wet bulb temperature
Coffee is prepared from coffee beans by leaching with
cold water
hot water
dilute hot caustic solution
naphtha
hot water
Gaseous diffusion co-efficient increases with increase in the
pressure
temperature
both (a) & (b)
neither (a) nor (b)
temperature
With increase in absolute humidity, the dew point of an unsaturated mixture of air and water vapor (at constant pressure and temperature)
increases
remains unchanged
decreases
decreases linearly
increases
If xD = overhead product molal composition and RD = reflux ratio, then slope and intercept of the operating line for rectifying section are respectively
Xd/Rd+1 , Rd/Rd+1
Rd/Rd+1 , Xd/Xd+1
Xd/Rd+1 , Rd+1/Rd
Rd/Rd+1 , Xd/Xd+1
Pick out the wrong statement. Raoult’s law does not apply, when the
size of component molecules are not equal.
attractive forces between like and unlike molecules in the solution are approximately equal.
component molecules are nonpolar.
chemical combination or molecular association between unlike molecules takes place in the formation of solution.
component molecules are nonpolar.
Water-ethyl alcohal solution can be concentrated (in respect of alcohal concentration) by __________ distillation.
atmospheric
vacuum
high pressure
none of these
vacuum
L/mGis the expression for
absorption factor
Brinkman number
slope of operating line in absorber
slope of operating line in stripper.
absorption factor
Extraction of pencillin employs a __________ extraction coloumn.
centrifugal
packed
plate
None of these.
centrifugal
In case of gases, the binary diffusivity is proportional to (where, P = pressure)
P
1/P
1/sqrtP
sqrtP
1/P
When the gas to be dissolved in liquid is a/an __________ then normally co-current adsorber are used.
mixture of two gases
pure gas
ideal gas
sparingly soluble gas
pure gas
Corresponding to Prandtl number in heat transfer, the dimensionless group in mass transfer is the __________ number.
Schmidt
Sherwood
Peclet
Stanton
Schmidt
If a two phase system is in physical equilibrium; then it means that, the
escaping tendency of each component from the liquid phase to the vapor phase is exactly equal to that from vapor phase to liquid phase.
temperature of the liquid phase is equal to that of the vapor phase.
total pressure throughout the liquid phase is equal to that throughout the vapor phase.
all (a), (b) and (c).
all (a), (b) and (c).
McCabe-Thiele method of binary distillation does not assume that the
sensible heat changes are negligible compared with latent heat changes.
molar latent heats of all components are equal.
heat of mixing is negligible.
none of these
none of these
(NSh/NRe.NSc) is termed in mass transfer operation as the
Stanton number
Peclet number
thermal diffusivity
momentum diffusivity
Stanton number
The Hatta number is important in
multicomponent distillation.
binary distillation.
gas absorption without chemical reaction.
gas absorption with chemical reaction.
gas absorption with chemical reaction.
When a multistage tray tower uses a minimum reflux ratio, it implies
infinite trays and maximum reboiler heat load.
infinite trays and minimum reboiler heat load.
minimum trays and minimum reboiler heat load.
minimum trays and maximum reboiler heat load
infinite trays and minimum reboiler heat load.
CO2 can be absorbed by
hot cupric oxide
heated charcoal
cold Ca(OH)2
alumina
heated charcoal
For the same process conditions, the reflux ratio of an unlagged distillation column
decreases in winter
increases in winter
increases in summer
none of these conditions
increases in winter
An ideal tower packing should not
have low weight per unit volume.
have large surface area per unit volume.
have large free cross-section.
hold up large amount of liquid in the packing.
hold up large amount of liquid in the packing.
Which of the following is a suitable absorbent for removal of H2S from natural gas ?
Vetrocoke solution
Monoethanol amine (MEA)
Dilute
Hot water
Monoethanol amine (MEA)
Acetone is to be removed from air in an isothermal dilute absorber using pure water as solvent. The incoming air contains 5 mole% of acetone (yin = 0.05). The design equation to be used for obtaining the number of trays (N) of the absorber is, N+2 = 6 log (yin/yout).For 98% recovery of acetone, the number of trays required is/are
1
8
9
10
9
Schimdt number and Lewis number for pure air at atmospheric conditions are respectively
< 1 and ≈ 1
1 and 0
>1 and ≈ 1
0 and ≈ 1
< 1 and ≈ 1
FIGURE
A
Molecular diffusion is caused by the
transfer of molecules from low concentration to high concentration region.
thermal energy of the molecules.
activation energy of the molecules.
potential energy of the molecules.
thermal energy of the molecules.
At __________ reflux, theoretical number of plates in a distillation coloumn is calculated using Fenske-Underwood equation.
operating
total
minimum
maximum permissible
total
Separation of a mixture of two gases by absorption in the liquid solvent depends upon the difference in their
viscosity
density
solubility
relative volatility
solubility
Components, having widely different boiling point in a binary mixture, can be separated using __________ distillation.
molecular
extractive
steam
simple
simple
Which of the following equipments is not used in liquid-liquid extraction ?
Pachuka tank
Agitated vessels
Centrifugal extractors
Packed towers
Pachuka tank
Pick out the wrong statement.
Packed towers are preferred for vacuum operation, because the pressure drop through the packing is less and they (packings) also lessen the possibility of tower wall collapse.
Packed towers are preferred over plate towers for handling corrosive and foamy liquids.
Diameter of randomly packed tower is normally more than 1.2 metres.
Due to uneven supply and improper distribution of liquid, problem of channeling, loading & flooding is generally encountered in packed towers.
Diameter of randomly packed tower is normally more than 1.2 metres.
Equilibrium-moisture curves of different solids
are different
are same
depend on the humidity of the gas
none of these
are different
Azeotropism for ethyl alcohol-water system disappears by
increasing temperature
decreasing pressure
increasing pressure
no means
decreasing pressure
Degree of freedom for leaching and solvent extraction process is
1
3
0
2
3
Diffusion co-efficient generally depends upon the temperature, pressure & the nature of the components of the system. Its dimension is not the same as that of the
mass transfer co-efficient.
thermal diffusivity.
kinematic viscosity.
volumetric diffusivity.
mass transfer co-efficient.
Equilibrium moisture of a solid is equal to the total moisture minus free moisture. Which of the following substances will have maxi-mum equilibrium moisture ?
Anthracite coal
Rag paper
Bamboo
Inorganic solids
Bamboo
In the absorption of ammonia in water, the main resistance to absorption is by the __________ phase.
liquid
gas
both (a) & (b)
neither (a) nor (b)
gas
Drying of refractory is normally carried out in a __________ dryer.
open pan
tray
rotary vacuum
truck/tunnel.
truck/tunnel.
The expression, ln(F/W) is
differential distillation equation
for NtoG in absorption for dilute mixture
slope of q-line in McCabe-Thiele method
for relative volatility
differential distillation equation
Heat sensitive materials with very high latent heat of vaporisation may be economically separated using
liquid extraction
distillation
evaporation
absorption
liquid extraction
When the solvent dissolves very little of solute, then
solvent of low latent heat of vaporisation should be used.
solvent of low freezing point should be used.
large quantity of solvent is required to extract the solute.
very small quantity of solvent is required.
large quantity of solvent is required to extract the solute.
An alkaline solution is used to reduce the concentration of carbon dioxide in a stream from 10% to 0.1% by absorption with irreversible chemical reaction. The overall number of transfer units based on gas phase is
9.21
4.605
100
0.001
4.605
HETP is numerically equal to HTU, only when the operating line
lies below the equilibrium line.
lies above the equilibrium line.
and equilibrium lines are parallel.
is far from the equilibrium line.
and equilibrium lines are parallel.
In a distillation operation, what is the effect of the temperature of the reflux stream (given below) on the condenser and reboiler loads ?
Reflux conditions:
(i) Reflux stream is completely liquid and is at its bubble point.
(ii) Reflux stream is below its bubble point.
Condenser and reboiler loads are the same in both the cases.
Reboiler load is the same in both the cases but condenser load is higher in case (ii).
Condenser load is the same in both the cases but reboiler load is higher in case (ii).
Both condenser and reboiler loads are higher in case (ii) as compared to case (i).
Both condenser and reboiler loads are higher in case (ii) as compared to case (i).
Steady state equimolal counter diffusion occurs in case of
leaching
absorption
binary phase distillation
liquid-liquid extraction
binary phase distillation
JD factor for mass transfer is a function of Reynolds number. Mass transfer by molecular diffusion from a single drop to surrounding still air is given by
Nsh = 2
Nst = 2
Nsc = 2
none of these
Nsh = 2
The relative saturation of an unsaturated mixture of gas and vapor is independent of the
nature of the vapor.
temperature of the mixture.
composition of the mixture.
none of these.
none of these.
The adiabatic saturation curve for a vapour-gas mixture is
straight line.
slightly concave upward.
slightly concave downward.
none of these.
slightly concave upward.
Pick out the wrong statement.
Cellulose acetate membranes are used in dialysis process.
Elutriation process refers to when the soluble material is largely concentrated on the surface of an insoluble solid and is simply washed off by the solvent.
‘Cascade’ means a group of stages interconnected so that various streams flow from one to another.
Zirconia probe is used for the humidity measurement.
Zirconia probe is used for the humidity measurement.
The value of NA/(NA + NB), for steady state equimolal counter diffusion of two gases ‘A’ and ‘B’ is
1
∞
0.5
2
∞
Drift in a cooling tower is
the water entrained by the circulating air.
dependent on the water lost by evaporation.
desirable.
all (a), (b) & (c).
the water entrained by the circulating air.
With increase in the concentration of the adsorbate, the integral heat of adsorption
increases.
decreases.
remains unchanged.
may increase or decrease ; depends on the type of adsorbate
decreases.
Small dia distillation column can be a
packed column
sieve tray
bubble cap
any of these
packed column
If mass diffusivity in a mixture is equal to the thermal diffusivity, then the Lewis number is
0
1
< 1
> 1
1
An air-water vapour mixture has a dry bulb temperature of 60°C and a dew point temperature of 40°C. The total pressure is 101.3 kPa and the vapour pressure of water at 40°C and 60°C are 7.30 kPa and 19.91 kPa respectively.The humidity of air sample expressed as kg of water vapour/kg of dry air is
0.048
0.079
0.122
0.152
0.152
__________ column is used in gas absorption process.
Wetted wall
Seive/perforated tray
Bubble cap
Packed
Packed
Nitrobenzene (boiling point = 210.6°C) is steam distilled at 1 atm pressure.Nitrobenzene will distill off __________ °C.
at < 100
at > 210.6
between 100 and 210
none of these
at < 100
Pick out the wrong statement.
With decrease in feed temperature, the number of plates required for binary distillation decreases for a given L/V ratio.
The extraction per unit of total height for a short packed column is more effective than for a tall column, in case of liquid-liquid extraction.
Natural draft cooling towers are made of ferro-concrete and its cross-section is wider at the bottom.
Vanderwall adsorption is also called chemisorption.
Vanderwall adsorption is also called chemisorption.
At what value of reflux ratio, number of theoretical plates in a distillation column is minimum ?
0
1
∞
< 1
∞
Batch tray dryers suffers from the disadvantage of
high maintenance cost.
non-uniform & low production rate.
high labour cost & low heat economy.
all ‘a’, ‘b’ & ‘c’.
high labour cost & low heat economy.
In a moderately sized packed absorption tower, channeling (which is most severe with stacked packings) can be minimised by taking the ratio of tower diameter to packing diameter
> 4 :1
< 8 : 1
> 8:1
< 6:1
> 8:1
__________ column is preferred to be used, when a high liquid hold up is required in a reactor for gas-liquid reaction.
Packed
Bubble
Spray
Tray
Bubble
The ‘shanks system’ of leaching (i.e., counter-current multiple contact leaching) is used for
recovery of tannis from the tree barks and woods.
leaching sodium nitrate from Chilean nitrate bearing rock.
both (a) and (b).
neither (a) nor (b).
both (a) and (b).
Penetration model (theory) for mass transfer was enunciated by
Danckwerts
Toor and Marchello
Higbie
Kissinevskii
Higbie
Surface renewal model of mass transfer was enunciated by
Toor and Marchello
Fick
Danckwerts
Stefan
Danckwerts
When the __________ the relative humidity of air decreases, despite an increase in the absolute humidity.
temperature rises
pressure rises
temperature falls
pressure falls
temperature rises
For turbulent mass transfer in pipes, the Sherwood number depends on the Reynolds number as
Re0.33
Re0.53
Re0.83
Re
Re0.83
The relative humidity of air decreases in-spite of an increase in the absolute humidity, when the
temperature rises.
pressure rises.
temperature falls.
pressure falls.
temperature rises.
Unit of molal diffusivity is
cm2/sec gm . mole
gm moles/cm2 . sec
gm moles/cm. sec
gm moles/cm2. sec
gm moles/cm. sec
The term “approach” in a cooling tower refers to the difference in the temperature of the
cold water leaving the tower and the wet bulb temperature of the surrounding air.
hot water entering the tower and the wet bulb temperature of the surrounding air.
hot water entering and the cooled water leaving the cooling tower.
none of these
cold water leaving the tower and the wet bulb temperature of the surrounding air.
Binary distillation involves the mass transfer by __________ at the gas-liquid interface.
unidirectional diffusion from liquid to gas phase
unidirectional diffusion from gas to liquid phase
either ‘a’ or ‘b’
a counter diffusion at an almost equal molar rate
a counter diffusion at an almost equal molar rate
